Before Ruby 3.0, open-uri used to overwrite Kernel#open with its own version which also supports reading from external URLs rather than simply opening local files or running commands.
Mixing those two use-cases was quite dangerous however and had the potential for serious vulnerabilities if the passed URL was not ensured to be safe everywhere (including third-party code using Kernel#open).
As such, this behavior to overwrite Kernel#open was deprecated in Ruby 2.7 and finally removed in Ruby 3.0. To open an external URL, you can use the following code instead:
URI.open("https://brandemia.org/sites/default/files/inline/images/firefox_logo.jpg")